Loosely-Separated "Sister" Namespaces in Java

Most modern programming systems such as Java allow us to link independently developed components together dynamically. This makes it possible to develop and deploy software on a per component basis. However, a number of Java developers have reported a problem, ironically called the version barrier, imposed by the strict separation of namespaces. The version barrier prohibits one component from passing an instance to another component if each component contains that class type. This paper introduces a novel concept for Java namespaces, called sister namespaces, to address this problem. Sister namespaces can relax the version barrier between components. The main purpose of this paper is to provide a mechanism for relaxing the version barrier, while still allowing type-safe instance accesses between components with negligible performance penalties in regular execution.